NSILA-s is an insulin-like peptide which reacts with its own receptor and the insulin receptor. NSILA-s is elevated in about 40% of patients with hypoglycemia and non-islet cell tumors. NSILA-s is low in hypopituitary loses of growth hormone (GH), however, NSILA-s does not appear to respond acutely to changes in endogenous GH. A method for purification of NSILA-s and related peptides has been developed, taking advantage of its endogenous binding protein. With this method, three active fractions of different mobility on polyacrylamide gels have been identified.